ITS#7515 mdb_dbi_open(): Also open in parent txns.

This makes aborting nested and non-nested txns more
similar: The new DBI is available to the surrounding
context (parent txn and MDB_env respectively).

libraries/liblmdb/lmdb.h

@@ -757,10 +757,15 @@ int  mdb_txn_renew(MDB_txn *txn);
 
 	/** @brief Open a database in the environment.
 	 *
-	 * The database handle may be discarded by calling #mdb_dbi_close().  The
+	 * The database handle may be discarded by calling #mdb_dbi_close().
+	 * It denotes the name and parameters of a database, independently of
+	 * whether such a database exists. It will not exist if the transaction
+	 * which created it aborted, nor if another process deleted it. The
 	 * database handle resides in the shared environment, it is not owned
 	 * by the given transaction. Only one thread should call this function;
 	 * it is not mutex-protected in a read-only transaction.
+	 * Preexisting transactions, other than the current transaction and
+	 * any parents, must not use the new handle. Nor must their children.
 	 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
 	 * must be called before opening the environment.
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()

libraries/liblmdb/mdb.c

@@ -6953,6 +6953,7 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 	MDB_val key, data;
 	MDB_dbi i;
 	MDB_cursor mc;
+	uint16_t mdflags;
 	int rc, dbflag, exact;
 	unsigned int unused = 0;
 	size_t len;
@@ -7035,12 +7036,19 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 		txn->mt_dbflags[slot] = dbflag;
 		memcpy(&txn->mt_dbs[slot], data.mv_data, sizeof(MDB_db));
 		*dbi = slot;
-		txn->mt_env->me_dbflags[slot] = txn->mt_dbs[slot].md_flags;
+		txn->mt_env->me_dbflags[slot] = mdflags = txn->mt_dbs[slot].md_flags;
 		mdb_default_cmp(txn, slot);
 		if (!unused) {
 			txn->mt_numdbs++;
 			txn->mt_env->me_numdbs++;
 		}
+		/* Open the DB in parent txns as well */
+		while ((txn = txn->mt_parent) != NULL) {
+			txn->mt_dbflags[slot] = DB_STALE;
+			txn->mt_dbs[slot].md_flags = mdflags;
+			if (!unused)
+				txn->mt_numdbs++;
+		}
 	}
 
 	return rc;